The emergence of high-density polynucleotide (eg DNA or RNA) array technology has transformed the basic concepts of genomics and protemics analysis. The transition from “dot blots” to “arrays on glass slides” and then to DNA microarrays (also known as DNA chips) has revolutionised the industry by making large-scale clinical diagnostic testing and screening processes realistic for practical applications. As is well-known, a typical microarray, with reactive sites in a predetermined configuration on a substrate, will exhibit a binding pattern when exposed to a sample with target nucleic acid fragments having a base sequence complementary to that of the capture fragments attached on the reactive sites. The binding pattern and the binding efficiency can be detected by optical or electronic methods when an appropriate detection mechanism is used, which may include for example fluorescent labeling, current detection or impedance measurement.
The use of electrically-assisted nucleic acid hybridization is a known technique in the analysis of biological samples containing DNA, e.g. blood, plasma, urine etc. Conventionally, a chip for DNA detection is formed from one of a variety of materials including glass, silica and metal. On the surface of the chip a number of electrical contacts are formed using known techniques. To detect a particular DNA sequence in a biological sample, capture probes consisting of complementary DNA fragments are attached to the chip surface by means of an attachment layer which is conventionally an agarose gel. If a biological sample contains the target DNA, the target DNA will bind to the complementary DNA fragments by hybridization, and various imaging techniques may be used to detect such hybridization and thus the presence in the sample of the target DNA.